Trivia: Rod Serling set up a practical joke on writer Richard Matheson when the two were flying to San Francisco aboard a propeller-driven plane. Serling collaborated with the airline to tape a poster blow-up of the "Nightmare" gremlin's ugly face to the outside of the plane window. Just as Serling prompted Matheson to open the curtain, however, the plane's engines and props fired up, blowing away both the poster and Serling's intended gag.

Trivia: Writer Richard Matheson says he was pleased with most of Twilight Zone's film version of his short story - except for the gremlin. He'd conceived it as a dark, creepy and nearly-invisible humanoid figure. "But this thing," he complains, "looked more like a panda bear."

When he introduces himself to Millicent inside the train station, Paul is wearing a dripping wet raincoat. It stays wet in the close-ups, but in the next several inter-cut two-shots, it's completely dry.